Abstract
A novel kind of fiber optic ultrasonic sensor based on matching fiber Bragg gratings (FBGs) is proposed and demonstrated. The sensors consist of a pair of matching FBGs fixed to a special bracket. The bracket plays a role in stretching and squeezing the FBGs, with the push–pull effect efficiently coupling the ultrasonic signal to the sensor, thus, improving the sensor’s sensitivity. Side-band filtering technology-based intensity interrogation was used to detect ultrasounds in water. With the synergic effect of the matching FBGs, the sensor performed with a high signal-to-noise ratio (56.9 dB at 300 KHz, 53 dB at 1 MHz and 31.8 dB at 5 MHz) and the observed ultrasonic sinusoidal signals were undistorted and distinguishable in the time domain.
Highlights
Maritime security is a very important topic within sea transportation, submerged navigation, and marine disaster prediction
The light entered FBG2 and the resulting reflection was transmitted into a photodiode (PD, New Focus, Shanghai, China) with a bandwidth of 10 MHz at a gain of 0 dBm
The central wavelength of FBG1 matches the central wavelength of FBG2, which gives rise to the maximum energy output
Summary
Maritime security is a very important topic within sea transportation, submerged navigation, and marine disaster prediction. Compared with conventional ultrasonic sensors, the advantages of fiber optic-based ultrasonic sensors far outweigh their disadvantages Are they suitable for broadband weak signal detection and long-term use in especially harsh environments, but they can realize the goal of networked detection and, improve detection efficiency [8,9]. This means that research on fiber optic-based ultrasonic sensors is significant in many fields. Compared to other fiber optic ultrasonic sensors, it has excellent ultrasonic sensitivity and the ultrasonic sinusoidal signals we detected were undistorted and distinguishable in the time domain
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